Phosphonic Acid Molecule-assisted Synthesis Of Rhodium And Iridium Nanostructures And Their Catalytic Properties

Precious metal rhodium(Rh)-based and iridium(Ir)-based nanomaterials have broad application prospects in the fields of organic catalysis and electrocatalysis due to their unique physicochemical properties.The design and synthesis of Rh-based and Irbased nanomaterials with different morphologies can effectively improve their catalytic performance.Especially,the small organic molecules assisted chemical reduction method is an important strategy for the synthesis of Rh-based and Ir-based nanomaterials with special morphologyies in recent years.In this thesis,we observed that small-molecule phosphonic acid can not only serve as complexing agent and morphology directing agent,but also can act as template to assist the synthesis of Rh and Ir nanomaterials with special morphology.Furthermore,the formation mechanism of these Rh and Ir nanomaterials were investigated,and their applications in organic catalysis and electrocatalysis were explored.The main research contents are as follows:(1)Due to the excellent catalytic activity and durability,the controllable synthesis of branched noble metal nanostructures has attracted great attention.In the work,a facile and effective complexation-reduction strategy is developed for synthesizing Rh nanodendrites with hippocampus tail-like branches(Rh-NDHTs),using N2H4·H2O as a reductant and multiphosphonate molecule with a small molecular weight as complexant and functional agent.During the synthesis,the coordination interaction between multiphosphonate and RhCl3,as well as the freshly formed Rh nanocrystals-catalyzed hydrazine decomposition reaction(H2NNH2=N2+2H2)play important roles for the generation of Rh-NDHTs.Meanwhile,the phosphonate functionalization of RhNDHTs is achieved simultaneously in the course of the synthesis,originating from the strong adsorption of multiphosphonate on the Rh surface.When used as a heterogeneous catalyst for the o-phenylenediamine oxidation reaction,the phosphonate functionalized Rh-NDHTs exhibit enhanced catalytic efficiency and durability compared with commercially available Rh nanocrystals,attributing to their unordinary morphological and interfacial properties.(2)Hierarchical porous precious metal-based nanosheets with ultrathin structures and highly exposed active surfaces are desirable in energy conversion technology,while robust synthetic strategies remain challenging.Here,we report a facile 1hydroxyethylidene-1,1-diphosphonic acid(HEDP)-mediated approach to synthesize hierarchical porous Rh nanosheets(HP-Rh NSs),following the formation mechanism of emulsion-induced soft template.When HP-Rh NSs are applied to the methanol oxidation reaction(MOR),abundant edge/grain-boundary atoms and the ultrathin porous structure endow HP-Rh NSs with a mass activity of 333 A g-1 at 0.63 V,which are 5.8-fold enhancements compared with traditional commercial Pt black(57.4 A g-1).Meanwhile,the peak potential of MOR on HP-Rh NSs is 0.2 V lower than that on commercial Pt black.(3)One-dimensionally(1D)hollow noble meal nanotubes are attracting continuous attention because of their huge potential applications in catalysis and electrocatalysis.Herein,we successfully synthesize hollow iridium nanotubes(Ir NTs)with the rough porous surface by the HEDP induced self-template method under hydrothermal conditions and investigate their electrocatalytic performance for oxygen evolution(OER)in an acidic electrolyte.The unique 1D and porous structure endow Ir NTs with big surface area,high conductivity,and optimal atom utilization efficiency.Consequently,Ir NTs exhibit significantly enhanced activity and durability for acidic OER compared with commercial Ir nanocrystals.Ir NTs only require the overpotential of 245 mV to deliver the current density of 10 mA cm-2,much lower than commercial Ir nanocrystals(297 mV).